Bi-layer etch stop process for defect reduction and via stress migration improvement

ABSTRACT

A method of forming a film stack in an integrated circuit, said method comprising depositing a layer of silicon carbide adjacent a first layer of dielectric material, depositing a layer of silicon nitride adjacent the layer of silicon carbide, and depositing a second layer of dielectric material adjacent the layer of silicon nitride.

This application is a divisional of application Ser. No. 10/857,150,filed May 28, 2004, now U.S. Pat. No. 7,199,047, issued on Apr. 3, 2007.

BACKGROUND

An integrated circuit dielectric stack may comprise multiple layers ofdielectric material. During fabrication of a dielectric stack, each ofthese layers of dielectric material is formed adjacent to another layerof material. Etch-stop layers generally are deposited between dielectriclayers for use during etch-stop processes. However, the bonding and filmproperties of various etch-stop layers and dielectric materials cancause various problems. Specifically, defects that form as a result ofpoor adhesion strength between etch-stop layers and layers of dielectricmaterial often delaminate (“peel off”) and spread throughout thedielectric stack, rendering useless a device comprising the dielectricstack.

“Via-stress migration” is another common problem attributable to thefilm properties of various etch-stop layers and layers of dielectricmaterial and commonly occurs during extended operation of a devicecomprising the etch-stop layers and dielectric material. Via-stressmigration may be induced by the stress of the films comprising thedielectric stack and electrically conductive metal lines (e.g., vias)encapsulated within the dielectric stack. The force exerted on metallines by the stress mismatch between the dielectric stack and the metallines gives rise to the accumulation of voids in the metal lines,thereby resulting in damaged metal lines. Damaged metal lines render thedevice useless.

BRIEF SUMMARY

The problems noted above are solved in large part by a method of forminga film stack in an integrated circuit, said method comprising a siliconcarbide and silicon nitride bi-layer etch stop stack that reduces oreliminates via-stress migration and the production and/or delaminationof defects. One exemplary embodiment may comprise depositing a layer ofsilicon carbide adjacent a first layer of dielectric material,depositing a layer of silicon nitride adjacent the layer of siliconcarbide, and depositing a second layer of dielectric material adjacentthe layer of silicon nitride.

BRIEF DESCRIPTION OF THE DRAWINGS

For a detailed description of exemplary embodiments of the invention,reference will now be made to the accompanying drawings in which:

FIG. 1 a shows a dielectric stack comprising a silicon carbide andsilicon nitride bi-layer etch stop stack that is fabricated inaccordance with a preferred embodiment of the invention; and

FIG. 1 b shows a process that implements the embodiment of FIG. 1 a.

NOTATION AND NOMENCLATURE

Certain terms are used throughout the following description and claimsto refer to particular system components. As one skilled in the art willappreciate, companies may refer to a component by different names. Thisdocument does not intend to distinguish between components that differin name but not function. In the following discussion and in the claims,the terms “including” and “comprising” are used in an open-endedfashion, and thus should be interpreted to mean “including, but notlimited to . . . ” Also, the term “couple” or “couples” is intended tomean either an indirect or direct electrical connection. Thus, if afirst device couples to a second device, that connection may be througha direct electrical connection, or through an indirect electricalconnection via other devices and connections. Further, the term“adjacent” is generally meant to be interpreted as “abutting” and/or“immediately next to,” although in some embodiments, the term may beinterpreted as “near” or “in close proximity to.” Thus, two adjacentitems may abut one another or be separated by an intermediate item.

DETAILED DESCRIPTION

The following discussion is directed to various embodiments of theinvention. Although one or more of these embodiments may be preferred,the embodiments disclosed should not be interpreted, or otherwise used,as limiting the scope of the disclosure, including the claims. Inaddition, one skilled in the art will understand that the followingdescription has broad application, and the discussion of any embodimentis meant only to be exemplary of that embodiment, and not intended tointimate that the scope of the disclosure, including the claims, islimited to that embodiment.

Described herein is a manufacturing process that reduces or eliminatesvia-stress migration and the formation of defects induced bydelamination of dielectric films. FIG. 1 a shows a cross-sectional viewof an integrated circuit dielectric stack 100 comprising, among variouslayers of metal, dielectric material and etch-stop layers, a film stack102. The film stack 102 preferably comprises a silicon carbide andsilicon nitride bi-layer etch stop stack 200 sandwiched between anorgano-silicate glass (“OSG”) layer 104 and a fluoro-silicate glass(“FSG”) layer 106. As described below, the bi-layer etch-stop stack 200reduces or eliminates the occurrence of via-stress migration and/or theformation of defects. As described herein, the silicon nitride layer 204of the stack 200 may considerably reduce the occurrence and/or severityof via-stress migration. The silicon carbide layer 202 of the stack 200substantially reduces the formation of the defects described above.

The adhesion strength between many etch-stop materials and OSG isgenerally poor, resulting in the formation of defects due todelamination. However, the adhesion strength between silicon carbide andOSG is considerably strong. Accordingly, the silicon carbide layer 202is deposited adjacent the OSG layer 104 to prevent the formation ofdefects due to delamination. In general, the silicon carbide layer 202may be relatively thin in comparison to the silicon nitride layer 204and still achieve substantial adhesion strength with the OSG layer 104.As previously explained, this adhesion strength prevents defectformation, even if the OSG layer 104/etch-stop stack 200 is exposed toambient conditions (e.g., ambient temperature, humidity) for a prolongedperiod of time. In a preferred embodiment, the silicon carbide layer 202may range between approximately 100 angstroms and approximately 300angstroms in thickness. In other embodiments, the silicon carbide layer202 thickness is equal to or less than approximately 300 angstroms,although the scope of this disclosure also encompasses silicon carbidelayers thicker than 300 angstroms. Furthermore, in some embodiments, thesilicon carbide layer 202 may be pre-treated with an appropriatesubstance (e.g., helium, ammonia) to improve the adhesive properties ofthe silicon carbide layer 202 and to remove at least some unwantedsubstances from the silicon carbide layer 202 (e.g., passivationchemicals) prior to deposition.

Via-stress migration usually occurs due to the inability of electricallyconductive metal lines to withstand forces induced by the surroundingdielectric material layers. Silicon nitride generally has lower stresslevels than silicon carbide and thus is better able to preserve thefunctional integrity of the vias. Accordingly, the silicon nitride layer204 is deposited adjacent, preferably abutting, the silicon carbidelayer 202 to prevent via-stress migration upon deposition of the FSGlayer 106. The silicon nitride layer 204 may be considerably thickerthan the silicon carbide layer 202, such that the bi-layer etch stopstack 200 is of a thickness appropriate for an etching process. In apreferred embodiment, the thickness of the silicon nitride layer 204 maybe between approximately 300 angstroms and approximately 900 angstroms.In other embodiments, the thickness of the silicon nitride layer 204 maybe approximately 500 angstroms, although thicker or thinner siliconnitride layers also may be used.

An exemplary process of forming the film stack 102 of FIG. 1 a is shownin FIG. 1 b. The process may be implemented by first depositing asilicon carbide material adjacent (e.g., abutting) a relativelylow-dielectric constant (“low-k”) dielectric material, such as the OSGdescribed above, or adjacent any suitable front-end material (block250). The low-k material and/or the front-end material may be less thanapproximately 15 kilo-angstroms and preferably range betweenapproximately 1 kilo-angstrom and approximately 15 kilo-angstroms inthickness. If OSG is used, the OSG may be deposited adjacent thedielectric stack using a Novellus® Sequel Chamber, although OSG or otherlow-k dielectric material may be deposited using any suitable chamber.The silicon carbide material may be deposited using a suitable AppliedMaterials® chamber or any appropriate chamber.

A silicon nitride material then may be deposited adjacent (e.g.,abutting) the silicon carbide material (block 252), so that a siliconcarbide and silicon nitride bi-layer etch stop stack is formed. Thesilicon nitride layer may be deposited using a Novellus® Sequel Chamberor any other suitable chamber. Finally, at block 254, a high-densityplasma fluoro-silicate glass, phospho-silicate glass or any othersuitable type of oxide film (e.g., plasma-enhanced FSG ortetraethylorthosilicate) is deposited adjacent (e.g., abutting) thesilicon carbide and silicon nitride bi-layer etch stop stack. In atleast some embodiments, this oxide film may have a thickness less thanapproximately 20 kilo-angstroms and further, preferably betweenapproximately 1 kilo-angstrom and approximately 20 kilo-angstroms. IfFSG is used, the FSG may be deposited using a Novellus® Speed Chamber,although FSG or any other type of oxide film may be deposited using anysuitable chamber and/or any suitable technique.

The above discussion is meant to be illustrative of the principles andvarious embodiments of the present invention. Numerous variations andmodifications will become apparent to those skilled in the art once theabove disclosure is fully appreciated. It is intended that the followingclaims be interpreted to embrace all such variations and modifications.

1. A film stack, comprising: a first layer of dielectric materialcomprising an organo-silicate glass; a layer of silicon carbide incontact with the first layer of dielectric material; a layer of siliconnitride in contact with the silicon carbide layer, wherein the siliconcarbide layer is relatively thin with respect to the silicon nitridelayer, and the silicon carbide layer is pre-treated on at least asilicon nitride facing surface thereof with a substance selected from agroup consisting of helium and ammonia, and wherein a combined thicknessof the layer of silicon carbide and layer of silicon nitride is of athickness suitable for an etching process; and a second layer ofdielectric material comprising a plasma-enhanced fluoro-silicate glassadjacent the silicon nitride layer, wherein an adhesion strength betweenthe organo-silicate glass and silicon carbide reduces delaminationeffects in the film stack and the layer of silicon nitride in contactwith the layer of silicon carbide reduces via-stress migration in thefilm stack.
 2. The stack of claim 1, wherein the silicon carbide layerhas a thickness less than approximately 300 angstroms.
 3. The stack ofclaim 1, wherein the silicon nitride layer has a thickness less thanapproximately 1 kilo-angstrom.
 4. The stack of claim 1, wherein thefirst layer of dielectric material has a thickness less thanapproximately 16 kilo-angstroms.
 5. The stack of claim 1, wherein thesecond layer of dielectric material has a thickness less thanapproximately 20 kilo-angstroms.